BOSTON (AP) -- The Boston Athletic Association sold out its first event since last month's marathon bombings in 13 hours Wednesday as 6,500 runners filled the field to support the organization and the victims of the attack on its flagship race.

''Thank you for all of the support, especially those who ran on April 15 and are coming back for this event (the 10k) on June 23,'' the B.A.A. posted on its Facebook page shortly after closing registration at 11:15 p.m. ''We are grateful to the running community and locals who entered today. Boston Strong! Boston Stands As One!''

The B.A.A. 10K, which began in 2011, had not sold out in either of its first two years. B.A.A. executive director Tom Grilk said the popularity of this year's race was consistent with the support he'd seen from runners and non-runners alike after two bombs killed three people and wounded hundreds more on Boylston Street on April 15.

''We're not going to give in to terror. They're going to stand up, show up and run,'' Grilk said Wednesday afternoon, when a few hundred spots in the 10K remained. ''I'm pleased to be part of a community that reacts that way.''

The B.A.A. has received what Grilk called overwhelming support following the bombing - actor Kevin Spacey stopped by the office last week - and runners have been among the most visible backers. Already-scheduled events dedicated their races to Boston, and new runs sprouted up to show support and raise money for the victims.

Grilk would not say yet what would be done at the B.A.A.'s own race. He also declined to comment on security measures for a course that travels two blocks from the Boylston Street bombing site.

''Everyone will have a heightened sense of security,'' Grilk said. ''In terms of what public safety officials will do, I can't say, and wouldn't.''

A 125-year-old organization that remains best known for its signature, 26.2-mile race, the B.A.A. expanded its calendar in 2001 to include a half-marathon and then added a 5K five years ago and a 10K in 2011. The three shorter races are combined into a distance medley, and those who run all three are eligible for prize money based on the combined times.

The inaugural B.A.A. 10K had a field of 3,656. There were 5,503 runners last year.